Not sure if it was league rules or just random but up till just a couple years ago, some teams counted turnstile clicks, and I think the Nats may have been one of them. I have a hazy memory of the Dodgers catching flack for claiming a 40k attendance or something when there were tumbleweeds floating around the upper deck, and then a few months later everyone was counting by tickets sold. No idea if those two are connected though!
All teams count both tickets sold and turnstile, but publicly report only tickets sold. Paid attendance is a critical metric that I'm pretty sure is consistently reported throughout the league since the league publishes those numbers (providing a rational for comparability). Turnstile (actual attendance) is closely monitored by all clubs and now with electronic ticketing they for the most part have more data than ever on each of us, all the better for trying to extract every last $ out of us.
But turnstile is used internally for management purposes and a carefully guarded secret apparently.
Remember some years ago the financial statements of certain clubs were leaked? Paid attendance was part of the audited financial statements, in this case see Note A of the Florida Marlins' financials for the years ended 2008 and 2009:
https://www.scribd.com/doc/68522486/Florida-Marlins-PDF?secret_password=ag3up080ci8qeydt0c4#fullscreen&from_embedDuring 2009 and 2008, attendance at the Marlins 79 and 81 home games totaled totaled 1,464,109 and 1,335,078 fans,respectively. The attendance is published by Major League Baseball and represents substantially the number of tickets sold.
